We read with great interest the recent article by Cornelius et al1 on sleep disorders of patients with voltage-gated potassium channel (VGKC) complex autoimmunity. They underlined that sleep abnormalities in VGKC complex autoimmunity were mostly unknown. Dream-enactment behavior occurred in 3 patients (60%) with limbic encephalitis, but none of them demonstrated rapid eye movement (REM) sleep–related abnormal behaviors by video polysomnography (PSG). Cornelius et al stated that assessment of REM sleep atonia was not possible in most of the patients because of insufficient REM sleep. Herein, we present a 62-year-old man with limbic encephalitis who was seropositive for the VGKC-Lgi1 antibody. He was admitted to the hospital with complaints of hypersomnolence and abnormal behavior during sleep for 5 months. He also had confusion and partial seizures. Brain magnetic resonance imaging showed bilateral hippocampal hyperintensity on T2-weighted imaging, sparing the brainstem. Serum biochemical test results were within normal limits except that the patient had hyponatremia. Blood and imaging test findings showed no malignancy. His full-night video electroencephalography (EEG)-PSG revealed low sleep efficiency (52%) and REM sleep (8%), mostly with phasic electromyography activity, but REM sleep behavior disorder (RBD) was not recorded. We continued video EEG-PSG recordings during the day. In this recording, REM sleep was markedly increased (70%) with sleep efficiency (64%). Multiple jerky and kicking-like behaviors were observed during REM sleep with phasic electromyographic activity. Simultaneous 32-channel EEG also did not show epileptiform activity. The diagnosis of limbic encephalitis was supported after finding of antibodies against the Lgi1 protein in the cerebrospinal fluid and sera samples. He was given intravenous immunoglobulin and methylprednisolone sequentially. After 1 month, we observed prominent improvement in his sleep-related disorders and cognitive dysfunction.